Optical transmission with lightwaves propagating through a transparent solid medium has recently been the subject of prominent development in the telecommunication field. Optical telecommunication networks employ optical waveguides called "optical fibers" because of their physical structure. These optical fibers, linking several end users, may be used to construct terminal networks of varying complexity.
When all terminals of such a network are linked to a single central node, then the network is called a "star" network. In the known types of such star networks, the sole central node to which all terminals are connected is either active or passive. In the first case, a representative active star node may be by a signal repeater or a switching network. In the second case, a representative passive star node may be an optical signal coupler--the optical signal coupler may be either reflective or transmissive.
In the usual type of star network which employs an optical signal coupler, the latter functions as a central star node, because it joins all the optical fibers that link the transmitters to the receivers of a plurality of terminals. In such a star network, however, if the sole star center node fails, is paralyzes the whole system served by the network.
Accordingly, in order to improve the network reliability and make it less sensitive to the failure of such a sole star center node, in accordance with the known prior art, the star center is duplicated, as are the respective links between the terminals and the duplicated central node.
Such a prior art solution has the drawback of halving the power of the signals between the terminals. Consequently, there is a loss of about three decibels in addition to path attenuation of the generic (single node star center) system.
This drawback is particularly burdensome in passive star networks, in which a single star center node already contributes an insertion loss of about 10 (log.sub.10 n) decibels, where n is the number of terminals.